Johnson Controls LX Series, User Manual

Page: 67 / 107

LX Series Unit Ventilator Controller User's Guide 67
When the network variable is marked as persistent, the network variable value is
written to Electronically Erasable Programmable Read-Only Memory (EEPROM).
Once written to EEPROM, the network variable value is preserved through power
outs and resets. Every time it receives a new network variable value, the new value
is written into EEPROM.
However, EEPROM only accepts a limited number of data writes. The number of
writes that EEPROM accepts is large, but it is still limited. If the network variable
input is constantly changing, the network variable could exhaust the ability of the
EEPROM to store it in permanent memory.
If the value of the network variable is constant, and if it is received on the network
input at a fixed time interval, this does not cause the EEPROM to write new data.
The EEPROM only writes new data when the data value changes.
For these reasons, network variables that change infrequently (for example,
nviSetPoint network variables) are better candidates for persistence than others.
Setting Units
Measurement units are shown at the bottom of the Unit Ventilator Controller
configuration wizard menu. Select measurement units before you perform any
other tasks. When you change the measurement units, all unsaved information you
have entered into Unit Ventilator Controller configuration wizard is lost.
If you are using Imperial units of measure (such as degrees Fahrenheit, inches of
water, and Btu), see the
Units in L
ON
W
ORKS
Networks section.
However, if you change your system measurement unit, all the SNVT format types
also change. The measurement unit you select in the wizard, either SI or Imperial,
has an effect on the nvoHwInputx SNVT format type. Once you configure an input
through the wizard and select a SNVT Type, the format type is written in the
database and a change of the system measurement unit no longer has an effect on
that network variable.
Note: To prevent accidental loss of information, click Apply frequently as you
move through the setup procedure. Clicking OK saves the information, but
closes the wizard window.
Input Configuration
When you configure inputs, you set the signal type, signal interpretation, and the
SNVT that transmits the information over the network. You can configure inputs
through the sensor configuration wizard. The sensor configuration wizard can be
launched from both the Unit Ventilator Controller configuration wizard and the
Hardware Input functional block.